1. Field of the Invention
The present invention relates to an electrolytic cation exchange membrane electrolytic cell. More particularly it relates to a cation exchange membrane electrolytic cell suitable for electrolysis of an aqueous solution of an electrolyte such as water, an acid, a base, an alkali metal halide or an alkali metal carbonate, and to an ion exchange membrane for the electrolytic cell.
2. Description of the Prior Art
As a process for producing an alkali metal hydroxide and chlorine by the electrolysis of the above mentioned aqueous solution, particularly an aqueous solution of an alkali metal chloride, a diaphragm method has now been used in place of a mercury method with a view to preventing environmental pollution. Further, in order to efficiently obtain an alkali metal hydroxide having a high purity in a high concentration, it has been proposed and put into practical use to employ an ion exchange membrane.
On the other hand, from the standpoint of energy saving, it is desired to minimize the cell voltage in the electrolysis of this type. For this purpose, various methods have been proposed. However, in some cases, the cell voltage reduction is not adequate and in other cases, the electrolytic cell tends to be intricate, and thus no adequately satisfactory solution has yet been made.
The present inventors have conducted a research with an aim to carry out electrolysis of an aqueous solution at a minimal load voltage, and as a result, it has been found that the above object can be accomplished with use of a cation exchange membrane having a gas and liquid permeable porous non-electrode or non-electrocatalytic layer on at least one side thereof. This has been made the subject matter of European Patent Publication No. 0029,751, (U.S. Ser. No. 205,567) and U.S. Ser. No. 355,312.
The effectiveness for reducing the cell voltage obtainable by the use of such a cation exchange membrane having a porous layer on its surface, varies depending upon the material constituting the porous layer, the porosity and the thickness of the layer. However, it is regarded as an unexpected phenomenon that good cell voltage reducing effectiveness is obtainable even when the porous layer is made of an electrically non-conductive material as will be described hereinafter, or that the cell voltage can be reduced even when such a cation exchange membrane is disposed with a space from the electrode, whereby the electrode may not necessarily be disposed in contact with the membrane.